There is a device for performing three-dimensional measurement in such a manner that a measuring object is irradiated with predetermined light and light scattered by the measuring object is detected. As such a three-dimensional measurement device, there has been known a measurement device (Patent Document 1) in which a measuring object is irradiated with a specific light pattern so that the shape or the like of the measuring object can be measured, or a measurement device using a time-of-flight method. In the former method, a change in the specific light pattern is measured to measure a distance between the measurement device and the measuring object at a plurality of places. On the other hand, in the time-of-flight method, illumination light is emitted to an object, and the light reflected from the object is then received by a light reception portion. Thus, time of flight of the light therebetween is measured to obtain distance information.
When a measuring object is irradiated with a specific light pattern or illumination light in these methods, a predetermined light pattern may be generated using a diffraction optical element so that the measuring object can be irradiated with the generated light pattern. In this configuration, the generated light pattern is defined as a group of light spots each having a light quantity not lower than a predetermined light quantity and generated by a plurality of diffracted lights. When the positions and light intensities of the light spots are controlled, the specific light pattern can be formed. In addition, when the light spots overlap one another, the light spots can form illumination light.
In order to perform detection with high detection sensitivity, it is preferably that the generated light pattern has a uniform light quantity within a detection surface.
However, when parallel light is incident on a diffraction optical element, 0th-order diffracted light may be emitted as light with a large light quantity. In such a case, there arises a problem that light spots of the other diffracted lights weaker than the 0th-order diffracted light cannot be recognized. Even when the gain is adjusted to be higher, there arises a problem that blur or the like occurs around a light spot of the 0th-order diffracted light so that the light spots of the other diffracted lights around the light spot of the 0th-order diffracted light cannot be recognized. As a configuration for suppressing occurrence of such 0th-diffracted light, there has been known a configuration in which a plurality of diffraction optical elements are stacked, for example, as disclosed in Patent Document 2.
In addition, as techniques related to the present invention, Patent Document 3 and Patent Document 4 suggest examples of optical elements in which a diffusion function and a diffractive lens function are integrated.